Why did income tax rates increase during world war 2?

According to Philip Scranton is University Board of Governors Professor, History of Industry and Technology, at Rutgers University, "the federal income tax’s “confiscatory” top rates coming out of World War II, which the Eisenhower Administration left in place into the 1960s. During the war, the top “marginal rate” was 94%, but 94% of what? Then as now, income tax rates moved up at distinct break points.In World War Two, tax law revisions increased the numbers of “those paying some income taxes” from 7% of the U.S. population (1940) to 64% by 1944."